Machine parts and apparatus intended for high temperature operation



Patented Feb. 25, 1935 "UNITED STATES .MACHINE PARTs AND APPARATUS IN- TENDED FOR HIGH TEMPERATURE or.

ERATION Fritz Rittershau sen and Heinz Korschan, Essen,

Germany, assignors to Fried. Krupp Aktiengesellschaft, Essen-on-the-Ruhr, Germany No Drawing. a, Application May 12, 1931, Serial No. 536,940. In Germany June 6, 1930 Claims.

This invention relates to machine parts and apparatus intended for operation upon metals heated to a high temperature, which causes the machine parts to be subjected in use to considerable variations in temperature. Examples of such machine parts are centrifugal casting moulds, and matrices, swaging sockets, rollers, pressing plungers and dies for use at high temperatures.-

For centrifugal casting moulds, that is to say for moulds for the production of gray cast iron pipes by the centrifugal casting process, chromium nickel or chromium molybdenum steel alloys of somewhat the following composition have hitherto been regarded as the most suitable materials:

(a) Chromium-nickel steel alloys containing about 0.3% carbon, about 1.5 to 2% nickel and about 0.5 to 1% chromium, and.

'(b) Chromium-molybdenum steel alloys containing about 0.3% carbon, about 1.0 to 1.3% chromium and about 0.35% molybdenum.

Extensive researches have, however, shown that the durability of centrifugal casting moulds can be increased up to 100% if they are made of steel alloys which contain up to about 0.3% carbon, more than about 2.1% chromium, more than about 0.15% molybdenum with or without an amount of nickel up to about 2%. Some or all of the molybdenum may be replaced by about twice as much tungsten.

The improvement in the durability of the centrifugal casting moulds is believed to be due to the fact that on account of the increased chr0- mium and reduced carbon content the occurrence on the surface of a network of cracks due to stresses set up by heat is retarded and reduced. The occurrence of these cracks in existing centrifugal casting moulds is a source of anxiety. The improvement is believed to be also due to the fact that even after the formation of the cracks they are practically prevented from spreading and enlarging themselves by virtue of the substantially higher yield point due to the higher chromium content and the addition of molybdenum. It is found that particularly durable centrifugal casting moulds can be produced if the moulds'during the process for improving their properties, i. e. during hardening and tempering, are tempered to about 700 C. and allowed to cool from this temperature in the furnace. This cooling in the furnace from about -700 C. results in the reduction of the internal nearly complete absence of stress in centrifugal I casting moulds produced in this way brings with it the advantage, which is very substantial in the production of centrifugal cast pipes, that the moulds are not distorted during the centrifugal process. I As a practical example of a composition spe cially suitable for the production of centrifugal casting moulds a steel alloy may be mentioned which contains about 0.16% carbon, about 2.4% chromium and 0.38% molybdenum with or without an amount of nickel up to about 0.5%. The addition of molybdenum can be replaced by an addition of tungsten twice as large, 1. e. by about 0.76% tungsten; it is also found to be advantageous to add up to about 0.4% vanadium for the purpose of further increasing the yield point.

The steel alloys mentioned above are not only suitable for the production of centrifugal casting moulds but also for the production of all those machine parts or apparatus which have to work at high temperatures and aresubjected to considerable temperature variations, that is to say for the production of such articles as pressing matrices, swaging sockets, rollers, pressing plungers and pressing dies for use at high temperatures.

As an example of a composition suitable for the production of a hot pressing die a steel alloy may be mentioned which contains about 0.21% carbon, about 2.53% chromium, about 0.42% molybdenum and about 0.28% vanadium. For hot rollers a steel alloy is particularly suitable for example which contains about 0.28% carv bon, about 2.01% chromium, about 1.08% nickel and about 0.48% molybdenum.

What we claim and desire to secure by Letters Patent is:-

1. Articles which in their normal use are subjected to high temperatures or large temperature variations, said articles being composed of a steel alloy containing up to about 0.3% carbon, 1 about 2.1 to 4.5% chromium, about 0.15 to 0.8% molybdenum, up to about 0.4% vanadium and up to 2% nickel. D

2. Articles as specified in claim 1 in which the molybdenum content is replaced at least partly by about twice as much tungsten.

3. As a new article of manufacture a centrifugal casting mould made from a steel alloy containing about 0.16% carbon, about 2.4% chromium and about 0.38% molybdenum.

4. As a new article of manufacture a centrifugal casting mould made from a steel alloy containingabout, 0.16% carbon, about 2.4% chromium, about 0.38% molybdenumand up to about 0.5% nickel. 5. A centrifugal casting mould composed of a steel alloy containing up to about 0.3% of car-,

bon, about 2.1 to 4.5% of chromium, and about 0.15 to 0.8% of molybdenum.

6. A centrifugal casting mould composed of a steel alloy containing up to about 0.3% of carbon,

about 2.1 to 4.5% of chromium, about 0.15 to 0.8% of molybdenum, and up to 2% of nickel.

'7. A centrifugal casting mould as specified in claim 5, in which the molybdenum content is replaced at least partly by about twice as much 15 tungsten.

8. A centrifugal casting mould as specified in claim 6, in which the molybdenum content is replaced at least partly by about twice as much tungsten.

9. A centrifugal casting mould composed of a steel alloy containing up to about 0.3% carbon, about 2.1 to 4.5% of chromium, about 0.15 to 0.8%

of molybdenum and up to about 0.4% of vanadium.

10. A centrifugal casting mould as specified in claim 9, in which the molybdenum content is replaced at least partly by about twice as much tungsten.

FRITZ RITIERSHAUSEN. HEINZ KQRSCHAN. 

